A first account of fossil centrohelid heliozoans from an ancient Eocene locality near the Arctic Circle in Canada.

Centrohelid heliozoans are non-motile, single-celled, heterotrophic protists with radiating filose pseudopodia used to capture food prey, that are common components of soil, marine, and freshwater environments. Centrohelids are characterized by a cell covering consisting of overlapping siliceous components referred to as scales that serve as the primary means to distinguish between genera and species. Given the widespread occurrence of heliozoans in aquatic habitats, and the fact that the siliceous scales can fossilize, it is surprising that these organisms have not been previously reported from the fossil record. A rich assemblage of exquisitely preserved fossil centrohelids, including 15 species from six genera, is reported from an early Eocene freshwater locality situated near the Arctic Circle in Canada. Of these, six are described as new species, Pterocystis giraffensis sp. nov., Quendis spatha sp. nov., Choanocystis bulla sp. nov., Raphidocystis reticula sp. nov., Raphidocystis eocenensis sp. nov., and Raphidocystis kanowa sp. nov. The morphologies of the fossil heliozoan scales were remarkably similar to modern congeners, highlighting evolutionary stasis with respect to scale structure over 48 Ma. This is the first account of heliozoans from the fossil record, and supports the idea that the origin of this clade is older than the Eocene.